Addendum to Saquon Barkley Analysis

About a couple of weeks ago, I penned a piece looking at Saquon Barkley's effectiveness through two seasons with the New York Giants. I concluded the post by acknowledging the idea that his lack of efficiency could be attributed to a lack of support via the offensive line in front of him and the Giants' ineffectiveness in the passing game. I thought I should do more than pay lip service to these two arguments so I dug into these ideas some more. To the first point, the Giants offensive line the past two regular seasons has been middling according to Pro Football Focus (see here and here). This argument might seem like an appeal to authority and lack any sort of rigor, but given the data on offensive line play that is available free to the public, there is not much more I can do. ESPN has a stat called pass block win rate that uses tracking data (that is not public) to gauge whether or not an offensive lineman "won" his block on a given play. This can be parleyed into a team ranking. The methodology for pass block win rate can be found here. In 2019 the Giants offensive line ranked 12th (I cannot find a full leader-board for 2018) . Obviously pass blocking is not run blocking, but it is a decent proxy for gauging offensive line ability. This recent post at Football Outsiders talks about the correlation between passing and rushing effectiveness and one of the theories posited is that the correlation can be attributed to offensive line play. Football Outsiders also puts out its own offensive line statistics for passing and rushing. In 2019, the Giants offensive line ranked 25th in adjusted line yards in the run game and 17th in adjusted sack rate allowed. In 2018, those ranks were 29th and 20th respectively. This paints a more grim picture, but on the whole, when looking at the three different sources the offensive line is middling. So not terrible.

To address the lack of an effective passing game, I would say that if Barkley is as amazing as his biggest supporters espouse he is, he should be elevating the level of the Giants offense despite porous quarterback play. But we know rushing success on its own has almost no relationship to overall offensive performance (see studies conducted on the interplay between passing, rushing, and offensive efficiency here and here and my own analysis here). So even if Barkley was very effective, it would not have much of an effect on the Giants ability to move the football down the field and piece together scoring drives.

Putting the idea of running back fungibility aside, I found there was not much evidence that Barkley was better than his peers and warranted a massive Christian McCaffrey extension within the next year. Isolating running back ability is always going to be difficult in a sport like football where there are 11 players on the offensive side and it is not clear how we should divvy up credit between those players. One thought I had was to look at something that running backs may have some control over, something that is independent of offensive line play: the ability to break tackles. For the past two seasons, pro-football-reference has given users access to some advanced stats via charting from Sportsradar. For ball-carriers, this includes the number of tackles they broke and the corresponding rate at which they do so. My theory was that if breaking tackles is something that is consistent year over year, maybe we can better understand which running backs are most effective independent of context. The issue is there is only two seasons worth of data, thus I had some sample size concerns. So any conclusions drawn from this analysis should be taken with a grain of salt. With that being said, let us dive into the data from the past two seasons.

I first looked at every ball-carrier with at least 140 carries (sort of arbitrary but I had to set the cut-off somewhere) the past two seasons and visualized their broken tackle rate in those two seasons.

I recommend clicking on the chart for more clarity. There is not much consistency, as I feared. When modelling the 2019 rates as a function of a the 2018 rates weighted by attempts across seasons, I yielded a correlation of just 0.095 (about 9.5 percent of the variation in the 2019 rates can be explained by variation in the 2018 rates). Looking at the scale of the axes, the rate at which ball-carriers break tackles is small, thus we run into the aforementioned issue of sample size. To attempt to remedy the issue, I tried regressing the rates by padding the 2018 broken tackle rate with samples of league average broken tackle rates (this is a fantastic primer on the technique used to study three point percentage in basketball). The goal was to obtain a better correlation after padding the statistic in question. So I padded the 2018 rates with 100, 200, 300, and 400 league average carries (note that the typical league leader in carries has around 300). The rate I used to pad the results was a broken tackle rate of 0.07 broken tackles per carry, which was the average in 2018. Upon doing so, I obtained correlations of 0.1055, 0.1043, 0.1031, and 0.1022 for rates with 100, 200, 300, and 400 padded carries respectively. So the correlation barely budged after padding and actually became less reliable as the number of league average carries added increased.

So what can we conclude? Using the data I had available, the rate at which ball-carriers break tackles in year N is not very predictive of the rate in year N+1. Referencing this stat as a means for determining the best backs is not justifiable. If I had more data, maybe I could find more signal. But with the evidence at hand, I cannot say broken tackle rate is meaningful. Interestingly, Barkley posted an elite rate his rookie year and broke the second most tackles total behind Derrick Henry, but was merely average in his second season. So upon further reflection, I still think there is no justification for the Giants to pay up for his services as his rookie contract sets to expire after the 2021 season.